Demonstrating the negligible contribution of optical ACS/HST galaxies to source-subtracted cosmic infrared background fluctuations in deep IRAC/Spitzer images

We study the possible contribution of optical galaxies detected with the {\it Hubble} ACS instrument to the near-IR cosmic infrared (CIB) fluctuations in deep {\it Spitzer} images. The {\it Spitzer} data used in this analysis are obtained in the course of the GOODS project from which we select four independent $10^\prime\times10^\prime$ regions observed at both 3.6 and 4.5 \um. ACS source catalogs for all of these areas are used to construct maps containing only their emissions in the ACS $B, V, i, z$-bands. We find that deep Spitzer data exhibit CIB fluctuations remaining after removal of foreground galaxies of a very different clustering pattern at both 3.6 and 4.5 \um than the ACS galaxies could contribute. We also find that there are very good correlations between the ACS galaxies and the {\it removed} galaxies in the Spitzer maps, but practically no correlations remain with the residual Spitzer maps used to identify the CIB fluctuations. These contributions become negligible on larger scales used to probe the CIB fluctuations arising from clustering. This means that the ACS galaxies cannot contribute to the large-scale CIB fluctuations found in the residual Spitzer data. The absence of their contributions also means that the CIB fluctuations arise at z\gsim 7.5 as the Lyman break of their sources must be redshifted past the longest ACS band, or the fluctuations have to originate in the more local but extremely low luminosity galaxies.Comment: Ap.J.Letters, in press. Minor revisions to mathc the accepted versio

Calibrating Array Detectors

The development of sensitive large format imaging arrays for the infrared promises to provide revolutionary capabilities for space astronomy. For example, the Infrared Array Camera (IRAC) on SIRTF will use four 256 x 256 arrays to provide background limited high spatial resolution images of the sky in the 3 to 8 micron spectral region. In order to reach the performance limits possible with this generation of sensitive detectors, calibration procedures must be developed so that uncertainties in detector calibration will always be dominated by photon statistics from the dark sky as a major system noise source. In the near infrared, where the faint extragalactic sky is observed through the scattered and reemitted zodiacal light from our solar system, calibration is particularly important. Faint sources must be detected on this brighter local foreground. We present a procedure for calibrating imaging systems and analyzing such data. In our approach, by proper choice of observing strategy, information about detector parameters is encoded in the sky measurements. Proper analysis allows us to simultaneously solve for sky brightness and detector parameters, and provides accurate formal error estimates. This approach allows us to extract the calibration from the observations themselves; little or no additional information is necessary to allow full interpretation of the data. Further, this approach allows refinement and verification of detector parameters during the mission, and thus does not depend on a priori knowledge of the system or ground calibration for interpretation of images.Comment: Scheduled for ApJS, June 2000 (16 pages, 3 JPEG figures

New measurements of cosmic infrared background fluctuations from early epochs

Cosmic infrared background fluctuations may contain measurable contribution from objects inaccessible to current telescopic studies, such as the first stars and other luminous objects in the first Gyr of the Universe's evolution. In an attempt to uncover this contribution we have analyzed the GOODS data obtained with the Spitzer IRAC instrument, which are deeper and cover larger scales than the Spitzer data we have previously analyzed. Here we report these new measurements of the cosmic infrared background (CIB) fluctuations remaining after removing cosmic sources to fainter levels than before. The remaining anisotropies on scales > 0.5 arcmin have a significant clustering component with a low shot-noise contribution. We show that these fluctuations cannot be accounted for by instrumental effects, nor by the Solar system and Galactic foreground emissions and must arise from extragalactic sources.Comment: Ap.J.Letters, in pres

Cosmic Infrared Background Fluctuations and Zodiacal Light

We have performed a specific observational test to measure the effect that the zodiacal light can have on measurements of the spatial fluctuations of the near-IR background. Previous estimates of possible fluctuations caused by zodiacal light have often been extrapolated from observations of the thermal emission at longer wavelengths and low angular resolution, or from IRAC observations of high latitude fields where zodiacal light is faint and not strongly varying with time. The new observations analyzed here target the COSMOS field, at low ecliptic latitude where the zodiacal light intensity varies by factors of $\sim2$ over the range of solar elongations at which the field can be observed. We find that the white noise component of the spatial power spectrum of the background is correlated with the modeled zodiacal light intensity. Roughly half of the measured white noise is correlated with the zodiacal light, but a more detailed interpretation of the white noise is hampered by systematic uncertainties that are evident in the zodiacal light model. At large angular scales ($\gtrsim100"$) where excess power above the white noise is observed, we find no correlation of the power with the modeled intensity of the zodiacal light. This test clearly indicates that the large scale power in the infrared background is not being caused by the zodiacal light.Comment: 17 pp. Accepted for publication in the Ap

Development of a general purpose airborne simulator

Variable stability system development for General Purpose Airborne Simulator /GPAS

The effects of Dipteran ectoparasitism on the growth and development of nestlings of the pearly-eyed thrasher (Margarops fuscatus) in the Luquillo Mountains, Puerto Rico

"In a rain forest population of the Pearly-eyed Thrasher instances of warble fly parasitism were found to be high. An average of 96.7% of all nests and 97.0% of all nestlings was parasitized during the 1981-82 breeding seasons. Almost 100% of the sampled nests were parasitized each month during the two year period. Although instances of parasitism were high throughout the study period, consequences of its temporal and spatial variability were noted among nests and nestlings, both within seasons and throughout seasons, and from year to year. Causes of this variability included fluctuations in the fly’s population, which tended to increase over the breeding season in response to rainfall. Undoubtedly many more exogenous factors such as microhabitat variability, temperature, and humidity attributed to the differences in the observed instances of ectoparasitism, but they were not closely monitored. The reproductive success of the sampled thrasher population was greatly reduced as a direct consequence of warble fly parasitism, with nestling mortality averaging 50% for the 1981-82 breeding seasons. Although sample sizes of naturally parasitized thrasher nests were small for the 1979-80 breeding seasons, nestling mortality caused by warble fly parasitism at those nests averaged 60% (77% and 43% respectively). Though nestling mortality averaged 60% it was considerably higher for the wetter 1979 season and lower for the drier 1980 season. Similarly, though nestling mortality averaged 50% for the 1981-82 breeding seasons, it was higher (56.7%) for the wetter 1981 season and lower (42.8%) for the drier 1982 breeding season. Spatial variability in the instances and impact of warble fly parasitism was shown to be influenced by the ovipositing patterns of the adult female flies, which shifted with the host's ontogeny (dorsal and anterior preference in hatchlings, changing to ventral and more extensive parasitism as feather tracts developed) and seasonally in response to the rapidly increasing fly populations. It was shown that parasitism did not have to be heavy to cause debility or even death in thrasher nestlings. Thrasher nestlings showed a mixture of both rapid and gradual growth characteristics. Development paralelled that of small open-nesting passerine species during the first 1.5 weeks when growth was maximum, and conformed more closely to the patterns of typically slow-growing cavity nesters during the last half of the nestling period. Warble fly parasitism affected younger (smaller) nestlings during the first 1.5 weeks of development and warble loads did not have to be heavy to cause significant retardation in growth and even death in young nestlings. Moderate (31-60 larvae per nestling) and heavy ( > 60 larvae per nestling) parasite loads caused retardation and death in older (2-3 week old) nestlings. This study showed that body mass is not always an accurate determinant of body growth. Examples of extraneous factors (i.e., fly larvae, large seeds, prey skeletal fragments) were shown to contribute greatly to increased body weights. Heavy parasitism in the Luquillo Mountains populations of the Pearly-eyed Thrasher was thought to be the result of an apparent increased contact between parasite and host, which resulted from the host's recent increase in density. Even though warble fly ectoparasitism may continue to significantly reduce thrasher numbers, there are signs that the host is adjusting to heavy parasitism and may continue to be found in abundance in the rain forest."--Summary.Includes bibliographical references